小行星带的质量影响附近行星上的生命体-凯发k8官网

小行星带的质量影响附近行星上的生命体
文章来源:未知 文章作者:enread 发布时间:2012-11-05 05:44 字体: [ ] 
(单词翻译:双击或拖选)
solar systems with life-bearing planets may be rare if they are dependent on the presence of 1(小行星) belts of just the right mass, according to a study by rebecca martin, a nasa sagan fellow from the university of colorado in 2, and 3 mario livio of the space telescope science institute in baltimore, md. they suggest that the size and location of an asteroid belt, shaped by the evolution of the sun's protoplanetary disk and by the gravitational influence of a nearby giant jupiter-like planet, may determine whether complex life will evolve on an earth-like planet.
 
this might sound surprising because 4 are considered a nuisance(讨厌的人) due to their potential to impact earth and trigger mass extinctions. but an emerging view proposes that asteroid collisions with planets may provide a boost to the birth and evolution of complex life.
 
asteroids may have delivered water and organic compounds to the early earth. according to the theory of 5 6(点断平衡说), occasional asteroid impacts might accelerate the rate of biological evolution by disrupting a planet's environment to the point where species must try new adaptation strategies.
 
the 7 based their conclusion on an analysis of theoretical models and archival observations of extrasolar jupiter-sized planets and 8 disks around young stars. "our study shows that only a tiny fraction of planetary systems observed to date seem to have giant planets in the right location to produce an asteroid belt of the appropriate size, offering the potential for life on a nearby rocky planet," said martin, the study's lead author. "our study suggests that our solar system may be rather special."
 
the findings will appear today in the monthly notices of the royal 9 society: letters (published by 10 university press).
 
martin and livio suggest that the location of an asteroid belt relative to a jupiter-like planet is not an accident. the asteroid belt in our solar system, located between mars and jupiter, is a region of millions of space rocks that sits near the "snow line," which marks the border of a cold region where 11 material such as water ice are far enough from the sun to remain intact. at the time when the giant planets in our solar system were forming, the region just beyond the snow line contained a 12 mix of ices, rock, and metals that provided enough material to build giant planets like jupiter.
 
when jupiter formed just beyond the snow line, its powerful gravity prevented nearby material inside its orbit from 13(聚结的) and building planets. instead, jupiter's influence caused the material to collide and break apart. these fragmented rocks settled into an asteroid belt around the sun.
 
"to have such ideal conditions you need a giant planet like jupiter that is just outside the asteroid belt [and] that migrated a little bit, but not through the belt," livio explained. "if a large planet like jupiter migrates through the belt, it would 14 the material. if, on the other hand, a large planet did not migrate(移动) at all, that, too, is not good because the asteroid belt would be too massive. there would be so much bombardment(轰炸,炮击) from asteroids that life may never evolve."


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1 uo1yd     
n.小行星;海盘车(动物)
参考例句:
  • astronomers have yet to witness an asteroid impact with another planet.天文学家还没有目击过小行星撞击其它行星。
  • it's very unlikely that an asteroid will crash into earth but the danger exists.小行星撞地球的可能性很小,但这样的危险还是存在的。
2 bnbzs     
n.巨砾;卵石,圆石
参考例句:
  • we all heaved together and removed the boulder.大家一齐用劲,把大石头搬开了。
  • he stepped clear of the boulder.他从大石头后面走了出来。
3 doeyh     
n.天文学家
参考例句:
  • a new star attracted the notice of the astronomer.新发现的一颗星引起了那位天文学家的注意。
  • he is reputed to have been a good astronomer.他以一个优秀的天文学者闻名于世。
4 d02ebba086eb60b6155b94e12649ff84     
n.小行星( asteroid的名词复数 );海盘车,海星
参考例句:
  • asteroids,also known as "minor planets",are numerous in the outer space. 小行星,亦称为“小型行星”,在外太空中不计其数。
  • most stars probably have their quota of planets, meteorids, comets, and asteroids. 多数恒星也许还拥有若干行星、流星、彗星和小行星。
5 7bd3039c345abccc3ac40a4e434df484     
v.(在文字中)加标点符号,加标点( punctuate的过去式和过去分词 );不时打断某事物
参考例句:
  • her speech was punctuated by bursts of applause. 她的讲演不时被阵阵掌声打断。
  • the audience punctuated his speech by outbursts of applause. 听众不时以阵阵掌声打断他的讲话。 来自《简明英汉词典》
6 jiazs     
n.平衡,均衡,相称,均势,平静
参考例句:
  • change in the world around us disturbs our inner equilibrium.我们周围世界的变化扰乱了我们内心的平静。
  • this is best expressed in the form of an equilibrium constant.这最好用平衡常数的形式来表示。
7 569155f16962e086bd7de77deceefcbd     
n.天文学者,天文学家( astronomer的名词复数 )
参考例句:
  • astronomers can accurately foretell the date,time,and length of future eclipses. 天文学家能精确地预告未来日食月食的日期、时刻和时长。 来自《简明英汉词典》
  • astronomers used to ask why only saturn has rings. 天文学家们过去一直感到奇怪,为什么只有土星有光环。 来自《简明英汉词典》
8 debris     
n.瓦砾堆,废墟,碎片
参考例句:
  • after the bombing there was a lot of debris everywhere.轰炸之后到处瓦砾成堆。
  • bacteria sticks to food debris in the teeth,causing decay.细菌附着在牙缝中的食物残渣上,导致蛀牙。
9 ketyo     
adj.天文学的,(数字)极大的
参考例句:
  • he was an expert on ancient chinese astronomical literature.他是研究中国古代天文学文献的专家。
  • houses in the village are selling for astronomical prices.乡村的房价正在飙升。
10 wmmz0a     
n.牛津(英国城市)
参考例句:
  • at present he has become a professor of chemistry at oxford.他现在已是牛津大学的化学教授了。
  • this is where the road to oxford joins the road to london.这是去牛津的路与去伦敦的路的汇合处。
11 tlqzq     
adj.反复无常的,挥发性的,稍纵即逝的,脾气火爆的;n.挥发性物质
参考例句:
  • with the markets being so volatile,investments are at great risk.由于市场那么变化不定,投资冒着很大的风险。
  • his character was weak and volatile.他这个人意志薄弱,喜怒无常。
12 aonzx     
a.密集的,稠密的,浓密的;密度大的
参考例句:
  • the general ambushed his troops in the dense woods. 将军把部队埋伏在浓密的树林里。
  • the path was completely covered by the dense foliage. 小路被树叶厚厚地盖了一层。
13 b795440b9ade4378fef3486b241378bc     
v.联合,合并( coalesce的现在分词 )
参考例句:
  • a mental model begins coalescing in their minds. 一个意识模型开始结合到他们的脑子里。 来自互联网
  • on the basis of coalescing this kind of element can separate oil from compressed air. 采用凝聚原理,分离压缩空气中的油份。 来自互联网
14 udwzt     
vt.撒,驱散,散开;散布/播;vi.分散,消散
参考例句:
  • you pile everything up and scatter things around.你把东西乱堆乱放。
  • small villages scatter at the foot of the mountain.村庄零零落落地散布在山脚下。
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